376 p. HERBERT CARPENTER. 



should be based on facts that are of primary importance in 

 Echinoderm morphology, viz. the radiate arrangement of the 

 vascular system. 



Most of the leading writers on the Crinoids have adopted this 

 idea, e.g. Messrs. Wachsmuth and Springer and Professor 

 Wetherby in America; the distinguished Swiss palaeontologist, 

 Mons. P. de Loriol; Professor M. Neumayr in Vienna; Dr. 

 Chr. Liitken in Copenhagen; and (with a slight modification) 

 Professor Zittel of Munich. The principle of it is that the true 

 basal plates are those which are interradial in position, and are 

 situated immediately beneath the radials. Should there be a 

 ring of radially situated plates separating these basals from the 

 top stem-joint, as in Encrinus, Extracrinus, Marsujpites, and 

 many Palseocrinoids, they are to be considered as an additional 

 element in the calyx, and are best termed under-basals or 

 Infrahasalia. 



The homology of the radials of a Crinoid with the oculars of 

 an Urchin is now universally admitted, and the plates beneath 

 them, the basals proper (subradials or parabasals of the old 

 nomenclature), are almost as universally regarded as homologous 

 with the genital plates of the Urchins. This view, however, has 

 recently been controverted by an authority which carries much 

 weight in all questions relating to Echinoderm morphology, viz. 

 that of Ludwig.^ The genital plates of an Urchin or Asterid 

 are regarded by him as equivalent to the orals of a Crinoid or 

 Ophiurid. I have already endeavoured to point out some of the 

 inconsistencies resulting from this mode of looking at things." 

 But although Ludwig has since published two papers bearing on 

 this subject, he has not attempted to meet my arguments. He 

 is, however, less dogmatic than before. We do not hear anything 

 more about an undoubted homology, but he simply refers to the 

 parallel he has drawn as being "meiner Ansicht nach;" and 

 some of the observations recorded in these later papers seem to 

 me to strengthen my position very considerably, as I shall now 

 endeavour to show. 



It will be remembered that in immediate contact with the 

 dorsocentral plate of Marmpites^ are the five under-basals, 



> " Ueber den primaren Steincanal der Criuoideen, nebst vergleicliend 

 Anatomischen Bemerkungen iiber die Echinodermen iiberliaupt," ' Zeit. f. 

 Wiss. Zool.,' Bd. xxxiv, pp. 318-332. 



2 This Journal, vol. xx, 1880, pp. 322-329. 



3 This Journal, vol. xviii, 1878, p. 358, fig. 3. I think it will be advan- 

 tageous to limit the name "dorsocentral" to the central plate in the 

 apical system of the Echinoderms, instead of using it as equivalent to the 

 ceutrodorsal of the Comatulfs. This is another structure altogether, being 

 merely the modified top stem-joint. 



